1. Field of the Invention
The present invention relates to an optimum radio communication method with a radio frame variable control and a radio communication system using the method.
2. Description of the Related Art
FIG. 1 is a diagram depicting a radio format of which specification is standardized by 3GPP (Third Generation Partnership Project) as an international standard of a third generation high-speed mobile communication system.
In FIG. 1, only the n-th frame is shown. This means that the (n−1)th frame and the (n+1)th frame, which are not illustrated, continue before and after the n-th frame.
In FIG. 1, a plurality if continuous or discontinuous areas are assigned in the vertical direction, that is the frequency axis direction. Since the frequency area is frequency-divided so that the phases are orthogonal to each other, interference does not occur.
In the horizontal direction, that is, in the time direction, a plurality of OFDM (Orthogonal Frequency Division Multiplex) symbols is disposed to constitute one frame.
Here one OFDM symbol corresponds to one TTI (Transmission Time Interval).
In the beginning of each frame in the time axis direction, a common pilot channel 1 and a control channel 2 are disposed in the frequency axis direction as a set. These are of the set corresponding to each user or to each different channel.
This common pilot channel 1 indicates the delimit of a sub-frame, and provides all the users with the timing to calculate SNR (Signal to Noise Ratio) and a receiving level using the pilot. The control channel 2 has a demodulated information corresponding to the modulation method of the signal data.
In this way, the conventional configuration uses a fixed frame format having common the pilot channel 1 and the control channel 2 for each frame.
If such a fixed frame format is used, however, it is difficult to respond appropriately in a mobile communication system, even if the line speed could be increased depending on the line status between the transmission side apparatus (base station) and the reception side apparatus (mobile terminal).
With the foregoing in view, the present applicant proposed to improve a channel estimation accuracy and improve the throughput of the entire base station by using an appropriate frame pattern (Japanese Patent Application Laid-Open No. 2005-345325).
This invention disclosed in Japanese Patent Application Laid-Open No. 2005-345325 however is for controlling the number of distributed pilot channels among the frames. For example, deterioration of the throughput of the base station is prevented by adjusting the number of pilot channel symbols for a terminal moving at a low-speed, or decreasing the number of distributed pilot channel symbols among the frames.